“position is the set of moves that have currency available to a player”

I think currency just means “have an in-game impact”.

For instance I might say “I move five feet forward”. In D&D that’s a move with specific in-game effects, which might officially put you in melee reach of someone, or move you out of same, or trigger a trap or whatever. In Apocalypse World it’s not a move at all, for the most part. Sure, I can construct a scenario where we have declared my character to be five feet away from something important, but mostly saying “I move five feet forward” doesn’t amount to anything in game terms.

So I think in this context that’s what currency is about. The second post in this series sort of spells it out (but could be confusing to a newbie… and indeed I’m a newbie so maybe I’m confused too).

This makes RQ go "But in both games it still has a fictional effect"... i.e. that you're five feet further forward.